How to Inspect a Used Yamaha Outboard Before You Buy

A 2012 F150, supposedly 400 hours, well cared for, fresh water only. Whether that's true is hard to see from the outside. The ECU knows more: how long the engine ran in each rpm range, which faults are stored and whether every cylinder responds when fired. With M-JET DIAGNOSTIC you read all of that yourself during the inspection, without a laptop and without hauling the engine to a shop first.

Before the first start

• Try to see the engine cold. An engine that's already warm can hide starting problems
• Plug in the dongle, key on, read the fault memory before anyone cranks it
• Look at engine hours by rpm and compare them with what the listing says
• Cold live data: engine temperature and intake air temperature should be close to ambient, plus battery voltage at rest

What an empty fault memory means

An empty memory is a good sign, but it's not proof. It can be cleared, even the night before you show up. A few entries on an older engine are normal, like an engine shut-off switch fault from a pulled lanyard or a one-time battery voltage dip. Pay closer attention to entries for the knock sensor, oil pressure sensor, overcooling, thermo switch, pulser coil or an intake air leak, and to anything that comes straight back after clearing.

In the water and under load

If you can, run the engine up to temperature in the water. Watch engine temperature in live data, water pressure if the engine measures it, and oil pressure on many engines from the F115 class up. Battery voltage should be higher with the engine running than at rest, otherwise the charging system isn't charging. Then, with the engine stopped, run a quick actuator test on the coils and injectors. A cylinder that doesn't respond is a solid point for negotiating. Once it's warm, watch the idle too. If rpm hunts, look at ISC valve opening and intake pressure in live data.

What you still have to check by hand

• Drain the gear oil. Milky oil means water in the lower unit
• The cooling water tell-tale stream with the engine running
• Compression test, all cylinders should be close to each other
• Anodes, paint and corrosion on the midsection, especially after salt water use
• Prop and prop shaft for dings and play
• Play in the steering and trim

When the seller won't play along

Some sellers don't want anyone plugging anything into their engine. The dongle doesn't change anything in the ECU as long as you only read and don't clear. Explain that up front. If they still say no, maybe they just don't like the idea, or maybe they have a reason. On a twin, read both engines, not just the one that sounds better.

Related topics

• Read Yamaha Outboard Engine Hours by RPM Range
• Read Yamaha Outboard Fault Codes with Your Phone
• Spring Commissioning a Yamaha Outboard After Winter Storage
• All Yamaha outboard diagnostics topics

Everything runs via app over Bluetooth, for Yamaha outboards with control unit generations from 2003. Learn more about the M-JET DIAGNOSTIC for Yamaha WaveRunner & Outboard.